This study involves the collaborative efforts of five centers and is being coordinated by the NIMH Psychopharmacology Research Branch (Dr. Robert Prien). The primary aims of the study are: 1) to compare the effectiveness of lithium carbonate, imipramine, placebo, and a combination of lithium and imipramine in the long-term maintenance treatment of unipolar recurrent affective illness (44 patients at each center); and 2) to compare the effectiveness of lithium carbonate, imipramine, and a combination of lithium and imipramine in the long-term maintenance treatment of bipolar recurrent affective illness (30 patients at each center). Secondary aims of the study are: 1) to identify demographic or clinical variables which are related to treatment outcome; 2) to determine whether the study treatments prevent or merely attenuate depressive and manic recurrences; and 3) to determine whether affective recurrences can be successfully treated by increasing the dose of maintenance medication.